Spectrally efficient fiber optics communications systems may evolve toward using differential phase shift keying (DPSK) modulation, differential quadrature phase shift keying (DQPSK) modulation, or both of a fiber optics signal. Detection of such a modulated signal may be achieved using either a twin photo-diode detector or a stacked photo-diode push-pull detector followed by a transimpedance amplifier (TIA). The stacked photo-diode push-pull detector may be preferable over the twin photo-diode detector due to ease of implementation and inherent match of adjacent monolithic photo-detectors, which may provide superior DPSK or DQPSK demodulation. However, when using the stacked photo-diode push-pull detector, for optimum performance, a TIA is needed that has both high input sensitivity and has linear push-pull input current handling capability. Further, fiber optics communications systems are evolving toward increasing data rates. Data rates above 100 gigabits-per-second (Gbps) are desirable. As such, a TIA is needed that operates at high data rates, has high input sensitivity, and has linear push-pull input current handling capability.
Present push-pull input TIAs may use complementary technologies that may limit data rates to less than 10 Gbps due to limited hole mobility of P-type metal-oxide-semiconductor (PMOS) or PNP transistor technologies. A common-emitter input TIA may eliminate the use of PMOS or PNP transistor technologies. However, such a TIA is a push only TIA that can accommodate only push input currents and cannot accommodate pull input currents without significantly degrading linearity. To provide pull input currents, a common-emitter input TIA may include a shunt input resistor in parallel with the stacked photo-diode push-pull detector to provide pull input currents. However, the shunt input resistor may contribute excessive input-referred current noise, which may degrade input sensitivity of the TIA. Alternatively, to provide pull input currents, the common-emitter input TIA may include a single-ended common-base input stage to provide input pull currents. However, the single-ended common-base input stage may require a large quiescent current that results in high input shot noise, which may degrade the input sensitivity of the TIA. As such, there remains a need for a TIA that operates at high data rates, has high input sensitivity, and has linear push-pull input current handling capability to provide linear amplification of a push-pull radio frequency (RF) input current signal.